I'm going to powering 4 peltiers (TEC1-12709 136.8W 12V 9A TEC) and I need to know what MOSFET type to use. I'm quite inexperienced with electronics so if you know a mosfet and model number I'd be super appreciative!

In series or in parallel? Using PWM? If so what frequency? Higher speeds of PWM would really need a MOSFET driver chip to get fast switching.

If you want to drive the MOSFET directly from an Arduino you _must_ get a logic-level FET.

What maximum current are you needing and what's the power supply(see my first question)? You need to calculatethe power dissipation in the FET using I-squared-R (ignore the nominal current rating of a MOSFET,its only applicable if using extreme cooling measures).

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In series or in parallel? Using PWM? If so what frequency? Higher speeds of PWM would really need a MOSFET driver chip to get fast switching.

If you want to drive the MOSFET directly from an Arduino you _must_ get a logic-level FET.

What maximum current are you needing and what's the power supply(see my first question)? You need to calculatethe power dissipation in the FET using I-squared-R (ignore the nominal current rating of a MOSFET,its only applicable if using extreme cooling measures).

Some of this has gone a bit over my head, this one of my first projects so apologies for my ignorance

The peltiers will be in Parallel, I don't know if I would be using PWM (should I use PWM?). Frequency wise I'm not sure.

Maximum current would be 28A, the power supply would be a max of 550W but in reality the power draw will be closer to 335W.

OK, so you need a very low Rds(on) device - heat dissipation is I-squared-R, so if the device were 10 milliohm thatwould be 8W dissipated when on, which would need a reasonable amount of cooling (something like a chipsetheatsink and fan perhaps?). If you got a 3 milliohm device you'd run a lot cooler or need less heatsinking.

I've used an IRLS3036 in the past, its logic level, has 60V rating and 2 milliohm. However its surface-mount only.

I'd recommend trying to get a device with Vds voltage rating of 20V or more, about 5 milliohm Rds(on) or thereaboutsand logic-level - TO220 package is probably easiest to heatsink (remember the drain terminal is also connected electricallyto the tab, so you need an insulating heat-conducting pad between package and heat-sink.

Another approach is to parallel a couple of devices to get half the Rds(on) figure - then 10 to 15 milliohm devices would be more feasible.

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OK, so you need a very low Rds(on) device - heat dissipation is I-squared-R, so if the device were 10 milliohm thatwould be 8W dissipated when on, which would need a reasonable amount of cooling (something like a chipsetheatsink and fan perhaps?). If you got a 3 milliohm device you'd run a lot cooler or need less heatsinking.

I've used an IRLS3036 in the past, its logic level, has 60V rating and 2 milliohm. However its surface-mount only.

I'd recommend trying to get a device with Vds voltage rating of 20V or more, about 5 milliohm Rds(on) or thereaboutsand logic-level - TO220 package is probably easiest to heatsink (remember the drain terminal is also connected electricallyto the tab, so you need an insulating heat-conducting pad between package and heat-sink.

Another approach is to parallel a couple of devices to get half the Rds(on) figure - then 10 to 15 milliohm devices would be more feasible.

Ok awesome, thanks for the help. Just to check so if I did a 2 x 2 series/ parallel then I would only need a mosfet rated for a 30V and 19A max correct?